Replaceable cartridges including machinery driven by a rotatable element are to be found, for example, in printer apparatus. In some types of electrophotographic printing apparatus, a replaceable binary ink dispersion cartridge (BID cartridge) is used to transfer toner to an electrostatically charged drum carrying a latent electrostatic image. The BID cartridge contains a mechanism for stirring the toner, in order to apply it homogeneously to the drum. In other embodiments of electrophotographic printing apparatus, the drum is comprised in the same cartridge as the toner. In that case, there is also a mechanism for rotating the drum.
The cartridge is replaceable because it contains components that wear out quickly and/or are consumed. When a new cartridge has been inserted into the apparatus, a so-called “soft start” is generally necessary. This is a method of driving the mechanism in the cartridge using an external drive according to particular characteristic programmed in the external drive control system. Generally, it involves driving the cartridge at a lower speed, allowing a component on a driven shaft to align correctly with a component on a shaft of the cartridge so that the two can engage to assume a state of readiness for driving at normal operating speeds. The soft start routines therefore involve a control system with a relatively elaborate and complicated implementation to effect this alignment.
It would, alternatively, be possible to engage a shaft of the cartridge by means of a clamping mechanism or some other kind of friction fit. This, however, makes removal of the cartridge more difficult, since such a connection would also lock the shaft in position in an axial direction (i.e. in a direction parallel to its rotation), the direction coinciding generally with the direction in which the cartridge is inserted in and withdrawn from the apparatus's housing.